Cellulose film treating system



Oct. 16, 1962 c. J. GONSALVES 3,058,151

CELLULOSE FILM TREATING SYSTEM Filed Aug. 30, 1960 IN V EN TOR.

CONRAD J OSEPH GONSALVES BYE; 2

ATTORNEYS United States Patent 3,058,151 CELLULOSE FlLM TREATHNG SYSTEMConrad Joseph Gonsalves, Arnhem, Netherlands, assignor to N.V.Onderzoekingsinstituut Research, Arnhem,

Netherlands, a corporation of the Netherlands Filed Aug. 30, 1960, Ser.No. 52,853 Claims priority, application Netherlands Sept. 26, 1956Claims. or. 18-15) This invention relates to a cellulose film treatingsystem, and relates more particularly to a method and apparatus for thetreatment of sheets, films and small ribbons of cellulosic material incontinuous form.

Cellulosic sheets, films and small ribbons, hereinafter referred to asfilms, are normally produced by extruding a suitable cellulosic solutionthrough a narrow slit or extrusion 'die of predetermined size and shapeinto a bath of liquid where coagulation or regeneration of thecellulosic solution takes place. While the method and apparatus of thisinvention are advantageous in the treatment of all kinds of films, theywill be described in con nection with the treatment of regeneratedcellulose films produced from viscose, but it is to be understood thatthis invention is not to be limited thereto.

In a prior method of producing regenerated cellulose film, a viscosesolution is extruded under pressure through a suitable orifice, such asa narrow slit or die of the desired shape, under the surface of a bathof coagulating liquid. From the coagulating bath, the resultant film issubjected to several subsequent operations; including purification andfinishing baths, usually over a system of guiding members in said latterbaths so that the film passes therethrough in a zig-zag path. The filmis then taken up on a suitable Winding device.

This and similar methods often have the disadvantage that the filmleaving each bath drags along from the bath an adherent liquid mantle.It is undesirable for several reasons that the liquid is taken along.Thus, the liquid which is taken from the bath must be replenished by newliquid by an amount which is generally greater than the amount requiredto replenish the bath as a result of the treatment of the film.Moreover, a part of the liquid taken out of the bath by the film willenter into the next treatment bath as a result of which this treatmentbath will be exhausted unduly rapidly. The latter will be more evidentin the case where, for instance, an acid and an alkaline bath directlysucceed each other. It is also undesirable for the film to carry alongbath liquid for the adherent liquid is never distributed over the filmin a uniform manner. Furthermore, the contacting time during which thefilm is subjected to the action of the bath liquid will not be the samein such a case for all parts of the film, and also the mechanical stresson the film is also uneven. As a result of this, difierences inproperties will occur between different parts of the film.

In order to overcome all of the foregoing disadvantages, methods anddevices have been proposed which were aimed to limit the quantity ofliquid which was taken out of the bath. For example, it was proposed topass the film as the film left the bath between two wipers made from aflexible material. In another expedient the film was passed through apair of squeezing rollers to squeeze out the excess of liquid. Both ofthese expedients had disadvantages. Thus, by the necessary contactbetween the wipers or the squeezing rollers and the film the danger waspresent that the film will be damaged. These damages were caused byunevenness in or at the surface of the wipers or rollers by which pitsor scratches were formed in the film surface.

Another disadvantage consists in that the wipers or the squeezingrollers give rise to an increase in tension in the moving film whichtension increase is detrimental to the film. In spinning a film fromviscose, the film leaving the coagulating bath is still soft;accordingly, it is desirable to keep the tension of the film as low aspossible to prevent undue strain thereon.

It is accordingly an object of this invention to provide an improvedmethod and apparatus for preparing film which will be free from theforegoing and other disadvantages.

Another object of this invention is the provision of an improved methodfor preparing film wherein the film leaving a treating bath has theliquid removed therefrom without damage to the film.

A further object of this invention is the provision of an improvedapparatus for removing liquid from film leaving a treating bath withoutdamage to the film and without undue tension thereon.

Still another object of this invention is the provision of films havingcharacteristics of uniformity and which are free from mechanical damage.

Other objects and advantages of this invention, together with certaindetails of construction and combinations of parts of the apparatus, willappear from the following detailed description.

The above objects are accomplished in accordance with this invention bypassing the film through the liquid coagulating or treating bath at highvelocity, preferably at a velocity of more than meters per minute, andthen, on leaving the bath, passing the film freely between a pair ofplates which extend across the whole width of the bath or at least areof substantially the same width as the film. The plates extend partlyinto the bath liquid at an angle to the surface thereof, and form, atleast with their lower edges, a narrow slit-shaped passage for the film.

It has been found that with a suificiently narrow adjustment of the slitand a sulficiently high film velocity at very satisfactory stripping ofthe adherent liquid mantle from the film is obtained. However, thevertical distance between the plates should be such that any directcontact between the film and the plates is avoided so that no dangerexists for mechanically damaging the film.

In addition to the holding back of the adherent liquid on the film, italso has been found that there is produced a very slight increase in thefilm tension. in many cases, however, the film tension is considerablyless than in the case where no measure whatsoever is taken in order toremove the adherent bath liquid.

It is necessary that the plates reach partly into the liquid of the bathand partly extend above the liquid surface thereof. The advantages ofapplicants invention will not be obtained if the plates are entirelysubmerged in the liquid or if they extend entirely above said liquid.

It has been surprisingly found that the narrowest slit width S betweenthe plates may not exceed a certain limit C If the width S of the slitremains below this limit C then on increasing the film velocity V therewill be reached a point where the liquid mass present between the plateswill suddenly disappear. Above this critical film velocity there is achange in the flow pattern of the liquid in and around the slit, and itappears that the plates surprisingly wipe almost the entire adherentliquid mantle from the film. 3

It has been found that this effect is obtained at a film velocity whichmeets the mathematical relation wlierein S represents the width of theslit, i.e. the distance between the plates at the point Where the slitis formed, which always has to be less than a critical value C andwherein C and C represent constants which in turn are functions of thethickness of the film, the nature of the surface of the film and theplates, the shape of the plates, the specific gravity and the viscosityof the liquid.

In practice, the constants C, and C may be easily determined by oneskilled in the art. For this purpose the width S of the slit is firstvaried at one definite high film velocity V until the width S equaling Chas been found, at which the liquid level in the slit between the platesgoes down. By subsequently varying the velocity V at a narroweradjustment of the width S of the slit until there is again the situationat which the liquid level in the slit goes down, the constant C may bedetermined so that for this case the critical width of the slit and thecritical film velocity are found. It has been found that the operablewidths of the slit need not be particularly narrow, nor do they need tomeet very strong requirements of accuracy. As a result a very goodwiping effect is readily obtainable with simple means.

The effect of the method of this invention may be strongly influenced bythe flow pattern of the liquid in the aftertreatment bath in thevicinity of the plates. Thus, it has been found that more adherentliquid is removed from the film with a less critical shape of the slitand at lower film velocities by suitably guiding the bath liquid.According to this invention it is preferred that at the lower edges ofthe plates the path of the liquid which does not pass the slit-shapedpassage is gradually deflected.

The apparatus for treating films in accordance with the method of thisinvention comprises a liquid container open at the top and with means inthe container for guiding the film through the liquid of the bath.

According to this invention, the apparatus is provided near the pointwhere the film leaves the liquid container and at either side of thefilm path two plates extending over the whole width of said film beingtreated, which plates partly reached into the bath liquid and whichform, at least with their submerged edges, a narrow slit-shaped passagefor the film. The plates extend partly above the liquid level in theliquid container.

As has been explained these plates serve as a wiper in a surprisinglysatisfactory manner at a certain adjustment of the slit width and at acertain film velocity. This effect is obtainable with flat as well ascurved plates and also with parallel as Well as a diverging arrangementof said plates.

According to apparatus of this invention, the desired action of theplates as wipers may be obtained most simply and also in the greatestdegree if the two plates are blade-shaped and have a form whichbeginning at the submerged edges of the plates gradually deflectupwardly from the film path.

It has been found that said films made by the method and apparatus ofthis invention show a greater uniformity and less mechanical damage thanfilms which have been manufactured according to usual methods.

In order to understand this invention more fully, reference is made tothe accompanying drawing in which:

The FIGURE is a vertical section or" an apparatus incorporating apreferred embodiment of this invention.

Referring to the figure of the drawing, a film 1 of regeneratedcellulose is formed by extruding a viscose solution through a castingslit 2 which is adapted to be submerged below the upper surface of aspinning or coagulating bath liquid held in a suitable container 4. Thecasting slit 2 is an element of a casting head 5, diagrammaticallyshown, to which viscose solution is supplied from a suitable sourcethrough a conduit 6. The formed film is passed substantially verticallydownward, then around guide rod 7 suitably mounted in the container 4after which it is passed upward in an oblique path. After leaving thespinning bath the film is passed via a deflecting or guide roller 8 toand through several aftertreatment baths (not shown) and finallycollected on a roller of a winding device (likewise not shown).

Two blade-shaped plates 9 and 10 are arranged across the whole width ofthe spinning bath or at least the whole width of the film 1 at the pointwhere the film leaves the spinning bath. These plates 9 and 10 form anupwardly broadening slit which is closed at either side by two sidewalls (not shown). The plates 9 and 10 are upwardly deflectedhorizontally according to a gradual profile and are thinly tapereddownwardly.

Specifically, where the film had a width of about 200 cm. at the plates9 and 10 and a thickness of about 0.15 mm., and the distance between theplates, ie the width of the slit, was 0.9 mm., it was found that with afilm velocity of 75 meters per minute the wedge-shaped space hounded bythe plates 9 and 10 was entirely filled with liquid. At the same time aquite considerable quantity of liquid was taken along by the film.

After the film velocity had been increased to 110 meters per minute, itwas found that the wedge-shaped space was entirely free from liquid andthat the liquid mantle entrained by the film was hardly perceptible.This was also accompanied by an especially uniform and turbulence-freeflow of bath liquid along the outer sides of the plates 9 and 10.

Film tensions measured behind the roller 8 were uniform and remained, onan average, at a lower level than the film tensions which were similarlyobserved in the absence of the plates 9 and 10. Moreover, in the lattercase the tensions being measured fluctuated to such an extend that itwas hardly possible to obtain what could be called an average filmtension.

An important advantage of this invention is that it provides a simpleand expeditious system of producing films having great uniformity ofthickness and free from physical imperfections.

While this invention has been described with particular reference to apreferred method of and apparatus for carrying out its practice, otherembodiments will be apparent to those skilled in the art. It istherefore intended to limit the invention only by the scope of theappended claims.

What is claimed is:

I. In a method of continuously passing a cellulose film through anaqueous liquid treating bath and out of the same, the steps of passingthe film through the liquid at a high velocity, and before removing thefilm from the liquid passing said film freely through a narrowhorizontal slit formed of spaced and substantially parallel surfacesextending across the whole width of the film and submerged only partlyin the liquid.

2. The method of claim 1 wherein the film passes though the liquid at avelocity of at least meters per minute.

3. In a. method of continuously passing film through a liquid treatingbath and out of the same, the steps of passing the film through theliquid at a high velocity, and before removing said film from liquid,passing the same freely through a horizontal slit formed of curvedspaced surfaces extending across the whole width of the film andsubmerged only partly in said liquid, the curvature of the surfacesbeing such as to cause the liquid not entering the slit to be deflected.

4. A device for wet treating cellulose films comprising a container forthe aqueous treating liquid, and, at a point where the treated film isadapted to leave the liquid container, two substantially parallelplates, of a width at least the width of the film, carried by saidcontainer, said plates being spaced from each other to form a narrowslit-shaped passage for the film, the construction and arrangement beingsuch that the plates only partly reach into the liquid of the container.

5. The device of claim 4, wherein the plates are curved, such as to forma narrow slit-shaped passage, which diverges from a constant widthprogressively in upward direction.

6. The device of claim 4, wherein a guide for the film is mounted in thecontainer in the prolongation of the slit-shaped passage.

7. A device for casting cellulosic films, comprising means for extrudinga viscose solution into a coagulating bath to form a film, a containerfor holding an aqueous coagulating liquid, a guide rod for guiding saidfilm mounted in said container and, at a point where the treated film isadapted to leave the liquid container, two substantially parallelplates, of a width at least the width of the film, carried by saidcontainer, said plates being 10 spaced from each other to form a narrowslit-shaped passage for the film, the construction and arrangement beingsuch that the guide rod is in the prolongation of the slit and that theplates only partly reach into the liquid of the container. I

References Cited in the file of this patent UNITED STATES PATENTS1,901,273 Taylor Mar. 14, 1933 2,062,795 Pike Dec. 1, 1936 2,536,093Coleman et al. Jan. 2, 1951 2,536,186 Keller Jan. 2, 1951 2,659,102Rarick Nov. 17, 1953 2,852,808 Sowter et a1. Sept. 23, 1958 2,914,419Oganowski Nov. 24, 1959 :UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,058,151 October 16, 1962 Conrad Joseph GonsalvesIt is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent shouldread ascorrected below.

In the heading to the printed specification, line date of priority, for"septa 26, 1956" read Sept. 26,.

(SEAL) Attest:

ESTON G. JOHNSON Attesting Officer DAVID L. LADD Commissioner of Patents

